Aerodynamic optimisation of vertical axis wind turbines using Adjoint methods in CFD

Vertical Axis Wind Turbines (VAWTs) have potential to provide a greater contribution to the deployment of wind energy around the world. At present however, progress is hindered by a massive shortfall in effectiveness of design methods associated with the complexity of VAWT aerodynamics. Predicting and designing for VAWT flows is not only an interesting technological challenge, but also one of great societal importance. If the performance and efficiency of VAWTs are improved, then their uptake and deployment around the world will be increased. Due to some key advantages of VAWTs, their widespread use in conjunction with Horizontal Axis Wind Turbines (HAWTs) could drastically improve the cost competitiveness of wind energy overall. This thesis describes the development of a new design/optimisation methodology that can be applied to VAWT aerodynamics. It is based on the powerful Adjoint method, which has been applied to other fields with great success. In the application of Adjoint methods to VAWT aerodynamics, this work shows an efficient new way to do VAWT blade shape optimisation. A 'semi-transient’ optimisation process is proposed, using Adjoint optimisation data from individual instances in time to improve VAWT performance. Such a method is novel in the field of VAWTs, and the use of Adjoint methods with low cost CFD models provides an efficient optimisation methodology that can be readily adopted by the VAWT design community. Throughout this work the commercial CFD software ANSYS Fluent (18.2) was used, although the proposed methodologies can be reproduced in other CFD codes which contain an Adjoint solver. This thesis opens an exciting new avenue of research departing from conventional parameter-based design methods, and the results show that Adjoint-optimised blades can provide significant increases to a VAWTs power coefficient. Discussion of these novel blade shapes also sheds new and important light on the flow physics and optimal blade geometries throughout the VAWTs revolution. Additionally, the results show that the semi-transient Adjoint method can be used to provide blades which greatly reduce the aerodynamic loading on the VAWT (and thus fatigue damage) whilst improving the average power coefficient.